Short-term water deprivation does not increase blood pressure variability or impair neurovascular function in healthy young adults

Abstract

High dietary salt increases arterial blood pressure variability (BPV) in salt-resistant, normotensive rodents and is thought to result from elevated plasma [Na+] sensitizing central sympathetic networks. Our purpose was to test the hypothesis that water deprivation (WD)-induced elevations in serum [Na+] augment BPV via changes in baroreflex function and sympathetic vascular transduction in humans. In a randomized crossover fashion, 35 adults [17 female/18 male, age: 25 ± 4 yr, systolic/diastolic blood pressure (BP): 107 ± 11/60 ± 7 mmHg, body mass index: 23 ± 3 kg/m2] completed two hydration protocols: a euhydration control condition (CON) and a stepwise reduction in water intake over 3 days, concluding with 16 h of WD. We assessed blood and urine electrolyte concentrations and osmolality, resting muscle sympathetic nerve activity (MSNA; peroneal microneurography; 18 paired recordings), beat-to-beat BP (photoplethysmography), common femoral artery blood flow (Doppler ultrasound), and heart rate (single-lead ECG). A subset of participants (n = 25) underwent ambulatory BP monitoring during day 3 of each protocol. We calculated average real variability as an index of BPV. WD increased serum [Na+] (141.0 ± 2.3 vs. 142.1 ± 1.7 mmol/L, P < 0.01) and plasma osmolality (288 ± 4 vs. 292 ± 5 mosmol/kg H2O, P < 0.01). However, WD did not increase beat-to-beat (1.9 ± 0.4 vs. 1.8 ± 0.4 mmHg, P = 0.24) or ambulatory daytime (9.6 ± 2.1 vs. 9.4 ± 3.3 mmHg, P = 0.76) systolic BPV. Additionally, sympathetic baroreflex sensitivity (P = 0.20) and sympathetic vascular transduction were not different after WD (P = 0.17 for peak Δmean BP following spontaneous MSNA bursts). These findings suggest that, despite modestly increasing serum [Na+], WD does not affect BPV, arterial baroreflex function, or sympathetic vascular transduction in healthy young adults.

Keywords: arterial baroreflex function; blood pressure variability; hypohydration; serum sodium concentrations; sympathetic vascular transduction.

Conflict of interest statement

No conflicts of interest, financial or otherwise, are declared by the authors.

Figures

Fig. 1.

In randomized crossover fashion, participants completed a euhydrated control condition (CON) and a water deprivation condition (WD) before laboratory testing on day 4. In the laboratory, we assessed heart rate, beat-to-beat blood pressure, common femoral artery diameter and blood flow, and muscle sympathetic nerve activity during 10 minutes of quiet rest in the supine position.

Fig. 2.

Summary data with individual data points are presented for beat-to-beat systolic arterial blood pressure (BP) average real variability (ARV) (A) and standard deviation (SD; B) during quiet rest in the supine position. Additionally, summary data with individual data points are presented for daytime ambulatory systolic BP ARV (C) and SD (D). Open bars indicate the normally hydrated control condition (CON), and filled bars indicate the water-deprived condition (WD). Data were compared with paired, 2-tailed t tests, with significance set at P < 0.05.

Fig. 3.

Summary data with individual data points are presented for the slopes of the linear regressions between muscle sympathetic nerve activity (MSNA) burst incidence and diastolic arterial blood pressure (BP; A) and total activity and diastolic BP (B) during quiet rest in the supine position. Open bars indicate the normally hydrated control condition (CON), and filled bars indicate the water-deprived condition (WD). Data were compared with paired, 2-tailed t tests, with significance set at P < 0.05. AU, arbitrary units. BRS, baroreflex sensitivity.

Fig. 4.

Summary data (means ± SD) are presented, showing the effect of spontaneous muscle sympathetic nerve activity (MSNA) bursts on mean arterial blood pressure (BP; A) and limb vascular conductance (LVC; C) over 10 cardiac cycles during quiet rest in the supine position. Additionally, summary data with individual data points are presented for peak absolute increases in mean BP (B) and peak %decreases in LVC (D) over the 10 cardiac cycles immediately following spontaneous MSNA bursts. ○ and open bars, normally hydrated control condition (CON); ● and filled bars, water-deprived condition (WD). Data were compared with 2-way (time × condition) repeated-measures ANOVAs (B and D) and paired, 2-tailed t tests (A and C), with significance set at P < 0.05. *Significant time effect.